The desirability of having the turnup portions of the carcass ply (or plies) of a pneumatic tire extend radially outwardly of the bead core the shortest possible distance is the premise on which prior art locked beads were developed. The proposed advantages included improved bead durability, and reduced material costs.
U.S. Pat. No. 4,922,985, issued May 8, 1990, discloses a carcass ply having a main portion that extends between both bead cores (not shown) of the tire and turnup portions that are anchored around each bead core. Tires according to U.S. Pat. No. 4,922,985 have the radially outer edges of the turnup portions of the carcass ply disposed radially outwardly of the bead cores a minimal distance and are in contact with the main portion of the carcass ply. Suitable elastomeric materials surround the bead core, carcass ply and other elastomeric components to complete the bead portion of the tire. In FIG. 4 of this patent, there is illustrated a clamping member comprised a strip of side-by-side cords of a heat shrinkable material embedded in a suitable elastomeric substance having a permanent thermal shrinkage of at least 2 percent. This strip of cords extended from a location radially and axially inward of the bead core to a location radially outward of the bead core and there was no filler strip or apex disposed between the main portion and turnup portion of the carcass ply.
Tires according to U.S. Pat. No. 4,922,985 were manufactured using a clamping member in which the heat shrinkable material was 1260/2 Nylon 6,6, having a permanent thermal shrinkage of about 4 percent. It is continually the goal in the art to simplify the construction and reduce the expense of building tires, yet improve the durability, handling, rolling resistance and other properties of tires.
In U.S. Pat. Nos. 5,524,688 and 6,719,030 pneumatic tires had two carcass plies or a single carcass ply reinforced with metallic cords, respectively. Each tire had a high ending ply turnup and locked bead construction.
The pneumatic tire 100 of U.S. Pat. No. 6,719,030 as shown in FIG. 7 had a single carcass ply 12 reinforced with parallel metallic cords, each cord composed of at least one filament having a tensile strength of at least (−2000.times.D+4400 MHa).times.95%, where D is the filament diameter in millimeters. The turnup portion of the single carcass ply in the bead portion of a pneumatic tire was interposed between the bead core and a toe guard, and the radially outer edge of each turnup portion being in contact with the main portion of the carcass ply and extending to an end point 0.5 to 4.0 inches (12.7 to 101.6 mm) radially outward of the bead core. The toe guard had a first and second end and each end was disposed directly adjacent to the carcass ply. The first end of the toe guard was located on the axially inner side of the main portion of the carcass ply at a location about 0.4 to 3.5 inches (10 to 89 mm) radially outward of the bead core and the second end was located at a point ranging from substantially the axially outermost point of the bead core to a location about 3.5 inches (89 mm) radially outward of the bead core. The first end and second end of the toe guard was a shorter distance from the bead core than the end point of the turnup portion of the carcass ply.
The toe guard may be a rubber material, a flexible textile material or a heat shrinkable material. For example, according to the embodiment illustrated in FIG. 7, the toeguard comprised a strip of side-by-side cords of a non-metallic heat shrinkable material which has a permanent thermal shrinkage of at least 2 percent wrapped circumferentially about the bead core and carcass ply turnup a plurality of times.
When the toeguard was disclosed as a rubber material it was disclosed to be canlendered gum strips circumferentially wound around the bed core and carcass ply turnups a plurality of times.
The use of separate stiffeners or apexes and chafer strips were shown to be used in combination with the plurality of windings of the gum strip used in the toeguard to form the bead portion of the tire.
The uses of multiple windings of strip of material wound around the green or uncured tire to form a carcass in cylindrical form can lead to variations in the rubber thicknesses and gauges around the circumference of the tire as it is shaped toroidally and placed in a mold to cure under temperature and pressure. In particular the area directly under the bead core. These anomalies can create mass imbalances and non-concentric positioning of the tire structure when mounted onto a rim, this resulting in undesirable force variations in tire as it rotates.
The present invention provides a novel way to eliminate the number of strips or rubber components in the bead portion of a tire using a non-cord reinforced toeguard.
The present invention by employing a unitary structure eliminates the non-uniformities created by the use of multiple strips of elastomeric components around the bead.
Thin and thick sections under the bead core and entrapped air problems associated with the use of multiple windings having step offs which create air pockets is eliminated in the tire bead area of the present invention tire.